Mercury arc rectifier with multiple grid structure



Dec. 24, 1968 SCHONHUBER ETAL 3,418,511

MERCURY ARC RECTIFIER WITH MULTIPLE GRID STRUCTURE Filed May 19. 1966 Kar Werner-Kanngiesser BY RU'MV IAIN-ML.

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United States Patent Office 3,418,511 Patented Dec. 24, 1968 3,418,511 MERCURY ARC RECTIFIER WITH MULTHLE GRID STRUCTURE Max Josef Schonhuber, Zurich, Switzerland, and Karl Werner Kanngiesser, Viernlreim, Hesse, Germany, assignors to Aktiengesellschaft Brown, Boveri & Cie, Baden, Switzerland, a joint-stock company Filed May 19, 1966, Ser. No. 551,403 Claims priority, application Switzerland, May 28, 1965, 7,474/65 6 Claims. (Cl. 313167) ABSTRACT OF THE DISCLOSURE A mercury arc rectifier is provided with a plurality of superposed identical grids arranged in such manner that the parallel bars of one grid are located in the spaces between the parallel bars of an adjacent grid. The spacing between adjacent bars of a grid does not exceed the width of the bars so that the anode will not be directly exposed to the cathode.

The present invention relates to an improvement in rectifiers of the mercury arc type and more particularly to an improved construction for such rectifiers as employ a plurality of grid elements.

It is known that such grids serve to control the ignition of arc rectifiers. However, they can, particularly in high tension rectifiers, also be used to control the potential distribution in the anode space. These grids have hitherto been made by drilling holes or milling slots into discs usually consisting of graphite, or in the form of cylindrical or basket-like plates. However, these forms of grid, while easy to produce, have the drawback thatespecially in high-tension rectifiersthe unavoidable edges formed by the solid parts between the holes may give rise to field intensities high enough to cause arc-back or arc-through. In order to avoid this, one would have to attempt, when using the known types of grids, to reduce the field intensity as much as possible by means of additional intermediate grids for potential control. But this necessitates a number of grids which increases with the voltage, with the result that the anode space has to be made unnecessarily large, entailing higher cost. According to the present invention the grids consist of bars of a cross-section which is at least partly rounded, the bars of one grid facing the interstices of its neighboring grid.

The bars may have a circular cross section of diameter preferably at least 0.5 cm., or they may be of elongated cross-section set edge-wise and having narrow sides rounded to a semicircular cross section.

Preferably the bars of a grid have their ends inserted in a carrier ring which is similarly rounded. The invention will :be further described with reference to the accompanying drawing which shows an example embodiment of the invention and in which:

FIG. 1 shows an electrode arrangement of a rectifier embodying the invention;

FIG. 2 is a plan view of a single grid; and

FIG. 3 is a view in central section on line 33 of FIG. 2.

With reference now to the drawings, and to FIG. 1 in particular, the depicted anode space of a mercury vapor arc rectifier is seen to include an anode 1 and superposed grids 2, 3 and 4.

These individual grids can be parts of the complete control grid, or they can serve for potential control only. The superposed planar grids 2 and 3 are bar type grids, each being comprised of a plurality of parallel spaced straight bars 5, of circular cross-section. Grid 4 is also comprised of a plurality of parallel spaced straight bars 6 but these bars are elongated in transverse section, the longer sides being parallel and flat and the shorter sides being rounded off to a semi-circular configuration. The bars 6 of grid 4 are oriented such that their longer dimension faces in the direction of the grid 3. The bars of the grids are arranged in an offset, staggered manner such that the bars of one grid, e.g. grid 2, are opposite the interstices between the bars of the adjacent grid, e.g. grid 3.

The rounded-peripheries of all bars have the advantage of avoiding high field concentrations as far as possible. For practical purposes, a bar diameter in the case of a cylindrical section 5, or edge radius in the case of an elongated section 6, of about 1 cm. is found to be a favorable value in the case of vessels used in high tension grid rectifiers. Like the known grids, the bars also consist of graphite. The grids can be provided with connection leads which are led out of the anode space by insulators and can be connected with a potential source via resistances, e.g. a potential divider. It is also possible to lead out connections from the individual bars and to give each bar a different potential. This is not shown in the drawing, since arrangements of this kind have already been provided in known grids.

It is evident from FIG. 1 that the spacing between adjacent bars has been made equal to the diameter of the bars. This spacing could be less than the bar diameter but, if possible, this spacing should not be exceeded, so that complete covering of the open cross-sectional area of the neighboring grids is attained. This complete covering prevents any mercury splashed into the grid space from penetrating to the anode. By this division of the control grid into several part grids the ignition voltage of the anode is reduced. Each part grid may have its own grid resistor, so that step-by-step firing of the whole grid is made possible, and the ionization can penetrate sufficiently far into the anode space even in the case of low anode voltages.

FIGS. 2 and 3 show one mode of fixing the bars 5. In these views, a bar grid is shown in plan and in cross section. The opposite ends of the :bars 5 are secured in place by a ring structure 8 which has a semi-circular contour 8a at its inner periphery. This ring type support can be made in any suitable manner to hold the bars. As depicted in FIG. 3, the ring is seen to be comprised of upper and lower half-rings 8b, including parallel spaced arcuate slots 9 in which the ends of the bars 5 are received. The ring halves 8b and 8c are secured together with the ends of the bars 5 clamped therebetween by means of any suitable clamping device. One of these may be used but preferably several may be spaced equally around the periphery of the ring 8. As depicted, the clamping device is seen to be comprised of a pair of angles. Corresponding sides 11 and 12 of these angles are arranged in parallel spaced relation so as to fit over the assembled ring halves 8b, 8c and assert a slight holding pressure on the bar ends, and suitable spacing means between the angle sides 11 and 12 is established by an insert block 13 to which the angles are secured by means of screws 14.

In lieu of an arcuate configuration for the slots 9 to receive the round ends of bars 5, the end portions of the bars 5 may be flattened and the slots in the ring 8 given a complementary configuration.

The carrier ring 8 for the bars 5 can be made partly of insulating material, or conducting material, depending upon whether the bars are to be electrically interconnected or insulated from one another.

With this arrangement it is possible to admit in mercury vapor arc rectifier vessels the inverse voltages which occur in very high tension direct voltage transmission, because high field concentrations in the vessel can be avoided without substantial increase of the electrode spacings. Besides, the risk of mercury droplets penetrating into the anode space is greatly minimized by the reduction of the distances between the bars and by the staggering of the grids.

We claim:

1. In a rectifier of the mercury vapor arc type having an anode space in which is positioned an anode and a grid structure adjacent thereto, the improvement wherein said grid structure is constituted by a plurality of superposed grids of identical construction, each said grid being comprised of a plurality of parallel spaced straight bars having a rounded configuration, and said grids being arranged such that the bars of adjacent grids are parallel to one another and also staggered so as to locate the bars of one grid opposite the interstices between the bars of an adjacent grid, the spacing between adjacent bars of 4 with the ends thereof rounded off-to substantially semicircular contour.

4. A mercury vapor arc rectifier as defined in claim 1 and which further includes a carrier ring for said bars, said carrier ring having a substantially semicircular contour at its inner periphery, and the opposite ends of said bars being received in openings provided in said carrier ring.

5. A vapor arc rectifier as defined in claim 4 wherein said openings in said carrier ring are constituted by slits and the end portions of said bars are correspondingly flattened for entry into said slits.

6. A mercury vapor arc rectifier as defined in claim 4 wherein said openings in said carrier ring have a configuration corresponding to the cross section of said bars.

References Cited UNITED STATES PATENTS..,

JAMES W. LAWRENCE, Primary Examiner. 7 P. C. DEMEO, Assistant Examiner.

US. Cl. X.R. 313195, 206, 348 

